RFR: JDK-8150496,(zipfs) Fix performance issues in zip-fs

[Peter Levart]

Hi Aleksey,


On 05/03/2016 02:39 PM, Aleksey Shipilev wrote:
> *) There is ever-so-subtle difference in doing either:
>
>   171             byte[] tmp = new byte[path.length + 1];
>   172             System.arraycopy(path, 0, tmp, 1, path.length);
>   173             tmp[0] = '/';
>
> ...or:
>
> 1083             byte[] name = new byte[nlen + 1];
> 1084             name[0] = '/';
> 1085             System.arraycopy(cen, pos + CENHDR, name, 1, nlen);
>
> Excess op between allocation and arraycopy breaks zeroing elimination,
> see e.g.:
>    http://cr.openjdk.java.net/~shade/scratch/ZeroingFirstBench.java

...so when allocation of array is immediately followed with arraycopy 
where the newly allocated array is the target, only the part of the 
array that is not overwritten by arraycopy will be zeroed? Because not 
the whole array is overwritten in your example/benchmark. That's good to 
know.

Regards, Peter